This invention relates generally to apparatus for providing thermal protection for hypervelocity vehicle structures that are subjected to aerodynamic heating during the flight profiles thereof.
In design of thermal protection systems (TPS) for aerospace vehicles, an effective means of transmitting aerodynamic loads (shear, and in some cases pressure differences) through the TPS is essential. That is, the load transfer system must have low weight, result in low thermal stresses, and not transfer excessive heat to the underlying structure.
Two primary approaches have previously been developed to satisfy these load-bearing and thermal isolation functions at low thermal stresses. One approach employs metal heat shields supported by slender metal stand-off supports that penetrate a nonload-bearing insulation. The flexible stand-offs of this prior art system bend as the shields expand on heating, thus imposing little restraint or thermal stress. This approach requires many small pieces forming a complex installation. The other approach employs a load-bearing insulation attached to the primary structure. Since most load-bearing insulations have low strength and no ductility, they are usually segmented with small gaps for low thermal stress. One load-bearing insulation previously developed includes the sintered quartz-fiber tiles now anticipated as the reusable surface insulation of the space shuttle. Generally, the nonmetallic insulations are simple to attach to the structure, but they have a common potential disadvantage. That is, they are weak, brittle materials, consequently, surface frayings, erosion, cracking or breakage rates may be high and may increase refurbishment requirements.
There is therefore a definite need in the art for an efficient thermal protection system that has the toughness of the metal shield systems and the simplicity of the load-bearing insulation systems.
Accordingly, it is an object of the present invention to provide a new and improved thermal protection system for hypervelocity vehicles.
Another object of the present invention is to provide new and novel insulating tiles for thermal protection of aerodynamic vehicles.
Another object of the present invention is to provide a thermal protection system for hypervelocity vehicle structures that is simple to refurbish but that normally requires little if any refurbishment.
An additional object of the present invention is to provide a new and novel assembly process for mechanically attaching insulating panels or tiles to a primary enclosure or vehicle structure.
The foregoing and other objects of the present invention are attained by providing the exterior surface portions of the hypervelocity vehicle to be protected in the form of a plurality of insulating multiwall panels or tiles mechanically attached to the primary vehicle structure. The primary vehicle structure may be of any conventional construction and is not alone considered as part of the present invention. The insulating multiwall tiles in one embodiment of the present invention are formed from multiple layers of metal foils that are alternately dimpled and nondimpled or smooth surface and joined at the dimpled contacts to form a strong insulation. The four edges of each tile are sealed and scarffed to minimize heat transfer through the panel edges. Each tile is attached to the primary vehicle structure by slip joints and a simple support. This attachment minimizes thermal stresses in the tiles and the primary vehicle structure. Also, vehicle structural strains are not transmitted to the tiles. No through fasteners are required except for the last tile in each row which is generally located at or near the top of the vehicle where less heating would be present for a particular fuselage station. Suitable felt seals are bonded to the periphery of each tile adjacent to the individual tile edges to prevent lateral flow of air into these spaces. The scarffed tile edges are sealed by metal strips with a vent being provided on the tile edge periphery and each tile edge beaded to inhibit air flow along the tile edges. Also, the two trailing edges of each tile overlap the two leading edges of the adjacent downstream tile or tiles.
For higher temperature applications an additional embodiment of the present invention utilizes metal foil inner and outer skin layers, joined at the peripheries by the beaded scarffed edge seals, sandwiching an interior layer of thermal insulation batts therebetween. And for even higher temperatures, the interior multiwall panel layer remains the same metal foil while the exterior layer is constructed of a silicide coated refractory metal waffle, such as for example, columbium. The sandwich interior of this embodiment is a layer of zirconia insulation disposed over a layer of thermal insulation, for example, microquartz. The attachment mechanism for each multiwall panel embodiment, to the hypervelocity vehicle, is identical.